[ToolboxItemAttribute(false)]
public class VisualWebPart1 : ContextualWebPart
{
    // Visual Studio might automatically update this path when you change the Visual Web Part project item.
    private const string _ascxPath = @"~/_CONTROLTEMPLATES/VisualWebPartTestProject/VisualWebPart2/VisualWebPart2UserControl.ascx";

    protected override void CreateChildControls()
    {
        Control control = Page.LoadControl(_ascxPath);
        Controls.Add(control);
    }

    public override ContextualGroupDefinition GetContextualGroupDefinition()
    {
        return new ContextualGroupDefinition()
        {
            Id = "TestContextualGroup",
            Title = "Contextual actions",
            Tabs = new TabDefinition[]
            {
                new TabDefinition()
                {
                    Id = "TestTab",
                    Title = "My tab",
                    Groups = new GroupDefinition[]
                    {
                        new GroupDefinition()
                        {
                            Id = "TestControlGroup",
                            Title = "Buttons group",
                            Template = GroupTemplateLibrary.SimpleTemplate,
                            Controls = new ControlDefinition[]
                            {
                                new ButtonDefinition()
                                {
                                    Id = "TestButton",
                                    Title = "Test alert",
                                    Image = new ImageDefinition() { Url32 = "/_layouts/images/erroricon.png" },
                                    CommandJavaScript = "alert('test')"
                                }
                            }

                        }
                    }
                }
            }
        };

    }
}